Breast milk and infant formula have different effects on gut bacteria

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Tessa Louwerens

Infant formula and breast milk both provide good bacteria for the intestinal tract of babies. However, the time at which certain bacteria colonise the intestines varies. These insights may be able to help manufacturers develop infant formula that is better for the health of the baby.

This was discovered by PhD candidate Klaudyna Borewicz of the Laboratory of Microbiology. In our bodies, specifically in the intestines, there are thousands of different species of bacteria. 'These are essential and play an important role in our health throughout our lives', says Borewicz, who received her PhD on 13 June. Borewicz investigated the effects of breast milk and infant formula on the bacteria in the intestines of the baby.

Stimulating 'good' bacteriaBacterial colonisation of the intestines begins prior to or during birth. Nutrition plays an important role in this process. Breast milk contains certain types of carbohydrates, called 'human milk oligosaccharides' (HMOs), which impact the composition of bacteria in the intestines. They primarily behave as prebiotics, substances that cannot be digested by the body, but are broken down by bacteria. Borewicz: 'We think that HMOs have evolved to stimulate the growth of ‘good bacteria’, which are advantageous for the developing baby.'

It is still not entirely clear what effect the prebiotics in breast milk and infant formula have on the bacteria in the intestines.

In order to mimic the beneficial effects of breast milk, manufacturers add prebiotics to infant formula as well. To do so, they use different carbohydrates, typically galactooligosaccharides or fructooligosaccharides. 'It is still not entirely clear what effect the prebiotics in breast milk and infant formula have on the bacteria in the intestines', explains Borewicz.

Breast milk cocktailIn order to solve the mystery, she studied nearly 200 mothers and their babies over a period of more than ten years. First, she looked at the composition of the breast milk and how this was correlated with the bacteria in the soiled diapers. There are actually more than 200 different HMOs and every mother produces a slightly different cocktail of them, which also changes over time. One of the things that Borewicz wanted to know was whether there was a specific HMO that could be singled out as particularly good at stimulating the growth of 'good bacteria'. However, she did not find it. 'It is more likely that it is a combination of many different components in breast milk.'

Infant formulaNext, Borewicz investigated the effect of infant formula, both with and without prebiotics. She discovered that the babies who were fed infant formula with prebiotics had the same quantities of the 'good bacteria' Bifidobacterium and Lactobacillus as the babies who were given breast milk. However, she also noticed that the colonisation took place in a slightly different way. In babies who were fed infant formula, the Bifidobacterium became well established in the intestines at an earlier stage. In babies who received both infant formula and breast milk, this occurred later on. 'We still do not know what effect this has on health', says Borewicz. Babies who were given traditional infant formula at the beginning of the study (without prebiotics) had fewer Bifidobacterium and more enterobacteria, which can cause illnesses.

Prebiotics, whether naturally occurring in breast milk or added to infant formula, not only have an impact on the types of bacteria in the intestines, but also on the time at which certain bacteria appear. Borewicz: 'We do not yet know exactly how this works and for the time being, it appears that it is best to breastfeed babies, if possible.'

In the future, infant formula manufacturers may be able to use these insights to create products that impact the bacterial composition of the intestinal tract. In doing so, they may eventually impact health in certain ways, such as reducing instances of asthma or allergies. Before that happens, Borewicz feels that it would be interesting to research the long-term effects which prebiotics in the milk have on health, e.g. how this corresponds to the predisposition for different illnesses.